1. Field of the Invention
The invention relates to wireless communications, and more particularly, to robustly updating the location of a wireless device within a wireless telecommunication system.
2. Description of the Related Art
Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002—A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005—A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 standard), and other standards. To the extent as known to one of skill in the art, these named standards are incorporated herein by reference.
Call setup is the process of establishing dedicated physical channels and negotiating service configuration parameters between a mobile station and a base station so that communication can take place. Call setup procedures fall into two classes. Mobile station originated call setup occurs when a mobile station user makes a call. Mobile station terminated call setup occurs when a call is made to the mobile station.
Call setup procedures involve signaling between a mobile switching center (MSC) or packet data service node (PDSN), one or more base stations (BS), and a mobile station (MS). As used herein, the term base station can be used interchangeably with the term access point. The term mobile station can be used interchangeably with the terms subscriber unit, subscriber station, access terminal, remote terminal, or other corresponding terms known in the art. The term mobile station encompasses fixed wireless applications. Signals from the mobile station are known as the reverse link, reverse channel, access channel, or reverse traffic. Signals to the mobile station are known as the forward link, forward channel, paging channel, or forward traffic.
Each step in the call setup procedures just described contributes to the call setup latency. Call setup latency, or the time required to set up a call, is an increasingly important parameter in wireless system design as data use becomes more prevalent. Modern wireless data communication systems offer “always on” connectivity. As those skilled in packet-switched network design know, “always on” connectivity does not mean a physical channel is permanently dedicated to a specific user. This would be bandwidth inefficient, and unlikely to be cost-effective for subscribers. Instead, when a mobile station engages in data communications, a call is setup to allow one or more packets to be transmitted, and then the call is torn down to free up the channel for another user. In a typical data communication session, calls will be set up and torn down repeatedly, with call setup latency occurring during each call. Naturally, decreasing call latency, while important in voice communications as well, is very important to provide a compelling user experience to the wireless data user.
Each step, described above, introduces latency due in part to the time required to transmit each message, and in part due to the processing time required to receive each message and determine the appropriate next step. Furthermore, much of the call setup signaling occurs on common channels which are shared by a number of mobile stations and a base station. As such, a component of the call setup latency is introduced when a mobile station must make repeated attempts to gain access to the common channel (known as the access channel). Furthermore, a message for a particular mobile station may have to be queued with messages for other mobile stations, yet another source of latency in performing the steps described above.
The latency issues of call setup may be compounded when the call setup occurs for a large group of wireless access terminals which are co-located within a small geographical area of a radio access network. As the number of access terminals in a particular geographic area increase, the time required to respond to a call setup request by the access terminals naturally increases because of the sudden, increased communications on the traffic channel. This may result in a sudden, uncontrolled request by a sufficient number of access terminals requesting call setup, called an ACK implosion. Maintaining the location of access terminals in a sector helps to reduce the probability of an ACK implosion.
As illustrated in FIG. 3, ACK implosion, as known in the prior art, resulting from a significant number of ACK responses to a call setup broadcast message may increase the collision probability on the access channel, thus increasing the latency, or wait time, for a call setup. Typically, a collision occurs when a device attempts to broadcast a packet during the same time that another device is broadcasting a packet. In FIG. 3, BS 302 broadcasts a call setup message via transceiver 304 to MS 306a-d. MS 306a-d may transmit a call setup ACK message back to BS 302 at nearly the same time, thus possibly resulting in an ACK implosion situation. If the ACK messages are transmitted at or nearly within the same time frame, the collision probably may be high, thus possibly resulting in multiple packet collisions. These multiple packet collisions may reduce the number call accept ACK messages sent by MS 306a-d that are received by BS 302. BS 302 may then need to re-broadcast the call setup message.
As described, call setup latency is formed through multiple message transmissions and corresponding acknowledgements, the length of each message, and the associated processing required with each message. Call setup latency is one cause of delay that is undesirable in many communication applications: voice communications as well as data communications. To the extent that multiple calls must be setup during a communication session, a typical scenario with data, the delay introduced is exacerbated.
This phenomenon causes an increase in the call setup times as the response to the call setup message is delayed. Scenarios in which a large group of wireless access terminals respond to a call setup message, in which the terminals are co-located within a small, geographic location, may include emergency situations such as public safety and disaster recovery operations. These scenarios call for effective and quick establishment of traffic channels for a large set of mobile devices. Latencies incurred during call setups for these large groups are as critical a metric as the efficiency in transporting media between these devices. Maintaining and updating the location of the mobile station may significantly reduce or eliminate the collision probability.
There is therefore a need in the art to update the location of mobile stations to reduce call setup latency.